PHOTOELECTRON-SPECTROSCOPY OF CO-N(-) AND PRODUCT ANIONS OF CO-N(-) WITH O-2 AND N-2

The photoelectron spectra of Co-n(-) (3 less than or equal to n less t han or equal to 70), ComN- and ComO- (3 less than or equal to m less t han or equal to 6) were measured by a XeCl excimer laser (4.025 eV). A lso the reactivities of Co-n(-) with O-2 and CO were measured. A clear distinction between the cluster size of n less than or equal to 6 and that of n greater than or equal to 7 was observed both in the photoel ectron spectra and in the reactivities. (i) In the size range above n = 7, the electron affinities of the cobalt clusters determined by the photoelectron spectra are linearly dependent on the reciprocal of the cluster radius, but below this size they deviate from this relation. ( ii) The reactivity of Co-n(-) with O-2 in the size range below n = 6 i s higher than that above n = 7. However, the reactivity with CO in the size range below n = 6 is extremely lower than that above n = 7. Thes e findings suggest that a transition of electronic structure in size d ependence, which is correlated with the reactivity, occurs at n simila r or equal to 7.